Refroidisseur 101 2021.02.07

REFROIDISSEUR 101

Présenté par: Emilie Boyer, ing.17 Février 2021

AGENDA

Les trois (3) configurations de base d’opération & de tuyauterie

Le syndrôme du faible Delta T et ses causes, effets et solutions

Les attentions particulières à porter sur un concept/débit. L’impact des températures de l’eau refroidie & celle du

condenseur sur la consommation d’énergie du refroidisseur. Les considérations à porter sur la conception afin de

minimiser la consommation d’énergie du système sans affecter les performance

Questions

2

1) ‘’Constant Primary Flow (CPF)’’

2) ‘’Primary / Secondary’’

3) ‘’Variable Primary Flow’’

Configurations de base

Secondary Pumps

Load = Flow XDeltaTConstant Primary Flow (CPF)Dedicated Pumping

4

Secondary Pumps

56 ºF(13.3 ºC)

56 ºF(13.3 ºC)

56 ºF(13.3 ºC)

(63 l/s) 44 ºF(6.7 ºC)

(189 l/s) @ 6.7 ºC)

(1760 kW)

(189 l/s) @ 13.3 ºC)

Constant Primary Flow at Design

Primary

5

Flow 3000gpm (189 l/s)

Delta T 12oF (6.7oC)

Per Chiller System

Load 500 Tons (1760kW)

1500 Tons (5280kW)

56 ºF(13.3 ºC)

Secondary Pumps

53 ºF(11.7 ºC)

53 ºF(11.7 ºC)

53 ºF(11.7 ºC)

(63 l/s)

(1760 kW)

53 ºF

75%

53 ºF

(189 l/s) @ 6.7 ºC)

Constant Primary Flow at 75% Load

Primary

(189 l/s) @ 11.7 ºC) (11.7 ºC)

6


Delta T 9oF (5.6oC)

Per Chiller System


1125 Tons (3960kW)

44 ºF(6.7 ºC)

56 ºF(13.3 ºC)

Secondary Pumps

50 ºF(10 ºC)

50 ºF(10 ºC)

50 ºF(10 ºC)

(63 l/s)

(1760 kW)

50 ºF

50%

50 ºF

(189 l/s) @ 6.7 ºC)

Constant Primary Flow at 50% Load All Pumps & Chillers On

Primary

(189 l/s) @ 10 ºC) (10 ºC)

7


Delta T 6oF (3.3oC)

Per Chiller System


750 Tons (2640kW)

44 ºF(6.7 ºC)

56 ºF(13.3 ºC)

Secondary Pumps

50 ºF(10.0 ºC)

50 ºF(10.0 ºC)

(63 l/s)

(1760 kW)

50 ºF

50%

50 ºF

(189 l/s) @ 8.3 ºC)

Constant Primary Flow at 50% Load 2 pumps on, 2 chillers on

Primary


Delta T 6oF (3.3oC)

Per Chiller System


500 Tons (1760kW)

56 ºF(13.3 ºC)

44 ºF(6.7 ºC)

44 ºF)

44 ºF (6.7 ºC)

44 ºF(6.7 ºC)

1000- GPM63- l/s

1000- GPM63- l/s

?? GPM?? l/s

2000

2000

126

(189 (10.0 ºC)126 l/s) @ 10.0 ºC)

8

Secondary Pumps

53 ºF(11.7 ºC)

53 ºF(11.7 ºC)

53 ºF(11.7 ºC)

(1760 kW)

50%

(189 l/s) @ 8.3 ºC)

Constant Primary Flow at 50% Load All pumps on, 2 chillers on

Primary


Delta T 6oF (3.3oC)

Per Chiller System


750 Tons (2640kW)

56 ºF(13.3 ºC)

47 ºF)

(63 l/s) 47 ºF(8.3 ºC)

53 ºF(189 l/s) @ 11.7 ºC)

53 ºF(11.7 ºC)

9

53 ºF(11.7 ºC)

44 ºF (6.7 ºC)

44 ºF (6.7 ºC)

Secondary Pumps

50 ºF(11.7 ºC)

50 ºF(11.7 ºC)

50 ºF(11.7 ºC)

(63 l/s)

(1760 kW)

50 ºF(11.7 ºC)

50%

(189 l/s) @ 11.7 ºC)50 ºF

(189 l/s) @ 6.7 ºC)

Constant Primary Flow at 50% LoadAll pumps on, 2 chillers on with CHW reset

Primary


Delta T 6oF (3.3oC)

Per Chiller System

Load 375 Tons 1320kW)

750 Tons (2640kW)

44 ºF(6.7 ºC)

56 ºF(13.3 ºC)

44 ºF)

50 ºF(11.7 ºC)

41 ºF (5.0 ºC)

41 ºF (5.0 ºC)

Need an automation System

12

Secondary Pumps

47 ºF(8.3 ºC)

47 ºF(8.3 ºC)

47 ºF (8.3ºC)

(63 l/s)

(1760 kW)

47 ºF(8.3 ºC)

25%

(189 l/s) @ 8.3 ºC)47 ºF

(189 l/s) @ 6.7 ºC)

Constant Primary Flow at 25% Load

Primary

11


Delta T 3oF (1.7oC)

Per Chiller System

Load 125 Tons (440kW) 375Tons (1320kW)

44 ºF(6.7 ºC)

56 ºF(13.3 ºC)

Advantages Lowest installed cost

Less plant space than P/S

Easy to Control & Operate

Easy to Commission

Disadvantages Highest Plant Energy Cost (all pumps on always, possibly chillers as well)

12

Constant Flow Primary

Primary (Constant) / Secondary (Variable)

PLoad = Flow XDeltaT

SLoad = Flow XDeltaT

Secondary Pumps

14

Primary (Constant) / Secondary (Variable)Headered Pumping

Secondary Pumps

15

But what controls the VSD’s?

16

What Controls the Flow of the Secondary Loop?

Valve Controls Leaving Air Temperature (LAT)

17

Valve Controls Leaving Air Temperature (LAT) Set Point = 55º (12.8º) LAT

T

18

As Valve Opens, Pressure in loop lowers As Valve Closes, Pressure in loop rises

19

T


T

20


T

21

Pressure Differential Sensor Controls Secondary Pump Speed

Differential Pressure sensor on last coil controls speed to Set Point (coil WPD+Valve PD+Piping PD+Safety) located at end of Index Circuit for best efficiency

Set PointP=25 ft (76 kPa)

P

22

Primary (Constant) / Secondary (Variable)Dedicated Pumping

Secondary Pumps

23

Primary (Constant) / Secondary (Variable)Rule of Flow

Primary flow must always be equal to or greater than Secondary flow.

Secondary Pumps

24

Primary/Secondary at Design

(63 l/s)

(1760 kW)

Secondary Pum3000 GPM @ 44

189 l/s @ 6.7 º

psºF

C

56 ºF(13.3 ºC)

56 ºF(13.3 ºC)

56 ºF(13.3 ºC)

56 ºF(13.3 ºC)(189 l/s) @ 13.3 ºC)

50 ft (152 kPa) Head

Per Chiller System

Load 500 Tons (1760kW) 1500 Tons (5280kW)

Primary Secondary Bypass

Flow 3000gpm (189 l/s) 3000gpm (189 l/s) 0gpm (0 l/s)

Delta T 12oF (6.7oC) 12oF (6.7oC) ----

0 GPM @ 44 ºF0 l/s @ 6.7 ºC

3000 GPM @ 56 ºF(189 l/s) @ 13.3 ºC)

44.0 °F (6.7 °C)

100 ft (303 kPa) Head

100% Load = 100% Sec Flow

25

Primary/Secondary at 75% Load

(63 l/s)

(1760 kW)

Secondary Pumps2250 GPM @ 44 ºF

142 l/s @ 6.7 ºC

53 ºF(11.7 ºC)

53 ºF(11.7 ºC)

53 ºF(11.7 ºC)

56 ºF(13.3 ºC)

Per Chiller System




Delta T 9oF (5oC) 12oF (6.7oC) ----

750 GPM @ 44 ºF47 l/s @ 6.7 ºC

75%

2250 GPM @ 56 ºF(142 l/s) @ 13.3 ºC)

3000 GPM @ 53 ºF(189 l/s) @ 11.7 ºC)

44.0 °F (6.7 °C)


26


(63 l/s)

(1760 kW)

Secondary Pumps 1500 GPM @ 44 ºF

95 l/s @ 6.7 ºC

53 ºF(11.7 ºC)

53 ºF(11.7 ºC)

56 ºF(13.3 ºC)

Per Chiller System





500 GPM @ 44 ºF32 l/s @ 6.7 ºC

50%

1500 GPM @ 56 ºF(95 l/s) @ 13.3 ºC)

2000 GPM @ 53 ºF(126 l/s) @ 11.7 ºC)

44.0 °F (6.7 °C)


27


(63 l/s)

(1760 kW)

Secondary Pumps 750 GPM @ 44 ºF

47 l/s @ 6.7 ºC

53 ºF(11.7 ºC)

56 ºF(13.3 ºC)

Per Chiller System





250 GPM @ 44 ºF16 l/s @ 6.7 ºC

25%

750 GPM @ 56 ºF(47l/s) @ 13.3 ºC)

1000 GPM @ 53 ºF(63 l/s) @ 11.7 ºC)

44.0 °F (6.7 °C)


28

Advantages Easy to Control

Easy to Commission

Loop separation

Easier trouble-shooting

Lower Plant Energy (can sequence chillers and ancillary equipment)

Versatile – multi-circuit capability

Lower pump energy cost than CPF

Disadvantages Highest Installed Cost (Sec Pumps, Piping, etc.)

Potential for higher plant energy loss because of Low Delta Tsyndrome

29

Primary (Constant) / Secondary (Variable)

Variable Primary Flow Load = Flow XDeltaT

Variable Primary Flow at 100% System Load

Two-way valves control capacity By varying flow of water in coils

Primary PumpsChillers Closed

31

Primary/Secondary System

Variable Primary System

Primary ChillersPumps

Four Differences?

32

Variable Primary Flow at Design

Variable Primary Flowat 100% System Load


Per Chiller System


Primary Bypass

Flow 3000gpm (189 l/s) 0gpm (0 l/s)

Delta T 12oF (6.7oC) ----

56 ºF(13.3 ºC)

0 GPM @ 44 ºF0 l/s @ 6.7 ºC

3000 GPM @ 56 ºF(189 l/s) @ 13.3 ºC)

44.0 °F(6.7 °C)

3000 GPM @ 56 ºF(189 l/s) @ 13.3 ºC)

Primary Pumps 1000 GPM each

(63 l/s)

500 Ton (1760 kW)Chillers

3000 GPM @ 44 ºF189 l/s @ 6.7 ºC

56 ºF(13.3 ºC)

56 ºF(13.3 ºC)

56 ºF(13.3 ºC)

Closed

100% Load = 100% Flow

33

Variable Primary Flow at 75% Load



Per Chiller System

Load 375 Tons (1320kW) 1125 Tons (3960 kW)

Primary Bypass

Flow 2250 gpm (189 l/s) 0 gpm (0 l/s)


56 ºF

0 GPM @ 44 ºF0 l/s @ 6.7 ºC

2250 GPM @ 56 ºF

44.0 °F(6.7 °C)

2250 GPM @ 56 ºF


(47 l/s)

2250 GPM @ 44 ºF142 l/s @ 6.7 ºC

56 ºF(13.3 ºC)

56 ºF(13.3 ºC)

56 ºF(13.3 ºC)

Closed

75% Load = 75% Flow

(142 l/s) @ 13.3 ºC) (142 l/s) @ 13.3 ºC) (13.3 ºC)

34




Per Chiller System


Primary Bypass

Flow 1500 gpm (95 l/s) 0 gpm (0 l/s)


56 ºF

0 GPM @ 44 ºF0 l/s @ 6.7 ºC

1500 GPM @ 56 ºF

44.0 °F(6.7 °C)

1500 GPM @ 56 ºF


(47 l/s)

1500 GPM @ 44 ºF95 l/s @ 6.7 ºC

56 ºF(13.3 ºC)

56 ºF(13.3 ºC)

Closed

50% Load = 50% Flow

(95 l/s) @ 13.3 ºC) (95 l/s) @ 13.3 ºC) (13.3 ºC)

35




Per Chiller System


Primary Bypass

Flow 750 gpm (95 l/s) 0 gpm (0 l/s)


56 ºF(13.3 ºC)

0 GPM @ 44 ºF0 l/s @ 6.7 ºC

750 GPM @ 56 ºF(47 l/s) @ 13.3 ºC)

44.0 °F(6.7 °C)

750 GPM @ 56 ºF(47 l/s) @ 13.3 ºC)

Primary Pumps 750 GPM(47 l/s)

750 GPM @ 44 ºF47 l/s @ 6.7 ºC

56 ºF(13.3 ºC)

Closed

25% Load = 25% Flow

38

Variable Primary Flow in Bypass Mode System flow below chiller min flow (250 gpm)



Per Chiller System

Load 50 Tons (176kW) 50Tons (176 kW)

Primary Bypass

Flow 250 gpm (95 l/s) 150 gpm (9.5 l/s)


56 ºF(13.3 ºC)

150 GPM @ 44 ºF

100 GPM @ 56 ºF(6.3 l/s) @ 13.3 ºC)

44.0 °F(6.7 °C)

250 GPM @ 48.8 ºF(15.8 l/s) @ 9.3 ºC)

Primary Pumps 250 GPM(15.8 l/s)

100 GPM @ 44 ºF6.3 l/s @ 6.7 ºC

9.5 l/s @ 6.7 ºCOpen

48.8 ºF (9.3 ºC)

37

Varying Flow Through Chillers - Issues

38

Issue 1 - During Normal Operation Chiller Type (centrifugal fast, absorbers slow)

System Water Volume (more water, more thermal capacitance, faster varianceallowed)

Active Loads (near or far from plant)

Typical VSD pump ramp rate setting of 10%/minute (accel/decel rates set to 600 seconds)

Issue 2 - Adding Chillers

Add chiller to sequence…operating chillers experience nuisance trips off-line(annoying)

Variable Primary System – Staging on chillers & changes in flow rateCurrent Situation – 1 chiller running



56 ºF(13.3 ºC)

44.0 °F (6.7 °C)

1000 GPM @ 56 ºF(63 l/s) @ 13.3 ºC)


(32 l/s)

1000 GPM @ 44 ºF63 l/s @ 6.7 ºC

Closed

Per Chiller System


39

Variable Primary System – Staging on chillers & changes in flow rateCurrent Situation –building load increases, valve opens, second chillerstarts



57 ºF(13.9 ºC)

45.0 °F (7.2 °C)

1100 GPM @ 57 ºF(69 l/s) @ 13.9 ºC)


(35 l/s)

1100 GPM @ 45 ºF69 l/s @ 7.2 ºC

Closed

Per Chiller System


40

Advantages Lower Installed Cost (approx. 5% compared P/S)

No secondary Pumps or piping, valves, electrical, installation, etc.

Less Plant Space Needed

Best Chilled Water Pump Energy Consumption (most optimization-ready configuration)

VSD energy savings

Lower potential impact from Low Delta T (can over pump chillers if needed)

Disadvantages Requires more robust (complex and properly calibrated) controlsystem Requires coordinated control of chillers, isolation valves, controls andpumps Potentially longer commissioning times to tune the system Need experienced facility manager to operate/maintain properly Not for every type of chillers (centrifugal vs absorption)

41

Variable Primary Flow (VPF) System Arrangement

AGENDA



Les attentions particulières à porter sur le concept & le débit.

L’impact des températures de l’eau refroidie & celle du condenseur sur la consommation d’énergie du refroidisseur.

Les considérations à porter sur la conception afin de minimiser la consommation d’énergie du système sans affecter les performance

Questions

42

Low Delta T Syndrome

Secondary Pumps

Design Delta T = 12ºF

44°F

43

56°F

Major Causes of Low Delta T

44

Dirty Coils

Chilled Water Coil

T

45

Chilled Water Coil

Load = Flow X Delta T

46

Primary/Secondary at DesignIdeal Operation

(63 l/s)

(1760 kW)


189 l/s @ 6.7 ºC

56 ºF(13.3 ºC)

56 ºF(13.3 ºC)

56 ºF(13.3 ºC)

56 ºF(13.3 ºC)(189 l/s) @ 13.3 ºC)

Per Chiller System



Flow 3000gpm (189 l/s) 3000gpm (189 l/s) 0 gpm (0 l/s)

Delta T 12oF (6.7oC) 12oF (6.7oC) ----

0 GPM @ 44 ºF0 l/s @ 6.7 ºC

3000 GPM @ 56 ºF(189 l/s) @ 13.3 ºC)

44.0 °F (6.7 °C)


12ºF (6.7ºC)

47

44 ºF(6.7 ºC)

Primary/Secondary at 67% LoadIdeal Operation

(63 l/s)

(1760 kW)


126 l/s @ 6.7 ºC

56 ºF(13.3 ºC)

56 ºF(13.3 ºC)

56 ºF(13.3 ºC)(189 l/s) @ 13.3 ºC)

Per Chiller System




Delta T 12oF (4.4oC) 12oF (6.7oC) ----

0 GPM @ 44 ºF0 l/s @ 6.7 ºC

2000 GPM @ 56 ºF(126 l/s) @ 13.3 ºC)

44.0 °F (6.7 °C)


2000 GPM @ 56 ºF(126 l/s) @ 13.3 ºC)

44 ºF(6.7 ºC)

12ºF (6.7ºC)

48

Primary/Secondary at 67% LoadLow DeltaT

(63 l/s)

(1760 kW)


152 l/s @ 6.7 ºC

54 ºF(12.2 ºC)

54 ºF(12.2 ºC)

54 ºF(12.2 ºC)(189 l/s) @ 13.3 ºC)

Per Chiller System



Flow 2000gpm (126 l/s) 2400gpm (152 l/s) 400 gpm (25l/s)

Delta T 10oF (5.6oC) 10oF (5.6oC) ----

400 GPM @ 54 ºF25.3 l/s @ 7.3 ºC

2400 GPM @ 54 ºF(152 l/s) @ 12.2 ºC)

44 °F(6.7 °C)


2000 GPM @ 54 ºF(126 l/s) @ 12.2 ºC)

44 ºF(6.7 ºC)

10ºF (5.6ºC)

49


(63 l/s)

(1760 kW)

Secondary Pumps2400 GPM @ 45.7 ºF

152 l/s @ 7.6 ºC

54 ºF ?(12.2 ºC ?)

54 ºF ?(12.2 ºC ?)

54 ºF ?(12.2 ºC ?)(189 l/s) @ 13.3 ºC)

Per Chiller System



Flow 2000gpm (126 l/s) 2400gpm (152 l/s) 400gpm (25l/s)

Delta T 10oF (5.6oC) 10oF (5.6oC) ----

400 ? GPM @ 54 ºF ?25.2 ?+ l/s @ 12.2 ºC ?

2400? GPM @ 54 ºF ?(152? l/s) @ 12.2 ºC ?)

45.7 °F (7.6 °C)


2000 GPM @ 54 ºF ?(126 l/s) @ 12.2 ºC ?)

45.7 ºF (7.6 ºC)

???

50


(63 l/s)

(1760 kW)


152 l/s @ 6.7 ºC

52 ºF(11.1 ºC)

52 ºF(11.1 ºC)

54 ºF(12.2 ºC)(189 l/s) @ 13.3 ºC)

Per Chiller System




Delta T 8oF (4.4oC) 10oF (5.6oC) ----

600 GPM @ 44 ºF38 l/s @ 6.7 ºC

2400 GPM @ 54 ºF(152 l/s) @ 12.2 ºC)

44 °F(6.7 °C)


3000 GPM @ 52 ºF(189 l/s) @ 11.1 ºC)

44 ºF(6.7 ºC)

10ºF (5.6ºC)

51

52 ºF(11.1 ºC)

Negative Effects of Low Delta T in P/S Systems

Consequences: Higher secondary pump energy

pumps run faster

Higher chilled water plant energy Ancillary equipment

Can’t load up chillers more than ratio Act DT / Des DT 10/12 = 83% or 417 tons

52

Variable Primary Flow at 67% LoadIdeal Operation



Per Chiller System


Primary Bypass

Flow 2000gpm (126l/s) 0gpm (0 l/s)


56 ºF(13.3 ºC)

0 GPM0 l/s

2000 GPM @ 56 ºF(126 l/s) @ 13.3 ºC)

44.0 °F(6.7 °C)

2000 GPM @ 56 ºF(126 l/s) @ 13.3 ºC)


(42 l/s)

500 Ton (1760 kW)Chillers

2000 GPM @ 44 ºF126 l/s @ 6.7 ºC

56 ºF(13.3 ºC)

56 ºF(13.3 ºC)

56 ºF(13.3 ºC)

Closed

67% Load = 67% Flow

53

Variable Primary Flow at 67% LoadLow DeltaT (can over-pump chillers)



Per Chiller System


Primary Bypass

Flow 2400gpm (152l/s) 400gpm (25 l/s)


54 ºF(12.2 ºC)

0 GPM0 l/s

2400 GPM @ 54 ºF(152 l/s) @ 12.2 ºC)

44.0 °F(6.7 °C)

2400 GPM @ 54 ºF(152 l/s) @ 12.2 ºC)


(51 l/s)

1200 GPM(76 l/s)

ea Chiller Flow

2400 GPM @ 44 ºF152 l/s @ 6.7 ºC

54 ºF(12.2 ºC)

54 ºF(12.2 ºC)

54 ºF(12.2 ºC)

Closed

67% Load = 80% Flow

54

Major Causes of Low Delta T

55

Dirty Coils

Controls Calibration

Leaky 2-Way Valves

Coils Piped-Up Backwards

Mixing 2-Way with 3-Way Valves in the same system

Solution to (or reduce effects of) Low Delta T

Address the causes Clean Coils

Calibrate controls periodically

Select proper 2W valves and maintain them (fix leaky valves)

No 3W valves in design

Find and correct piping installation errors

Over deltaT chillers by resetting supply water down (P/S)

56

AGENDA






Questions

57

58

Chillers Equal Sized Chillers preferred, but not required

Maintain Min flow rates with Bypass control (1.5 fps for flooded and 1 gpm/ton forDX)

Maintain Max flow rates (12.0 fps) and max WPDs (45’ for 2P, 67’ for3P)

Modulating Isolation Valves (or 2-positionstroke-able) set to open in 1.5 to 2 min

Don’t vary flow too quickly through chillers (VSD pump Ramp rate – typical setting of10%/min)

Sequence

If CSD Chillers – Load-based sequencing…run chillers to max load (Supply Temp rise). Do not run more chillers than needed

Load-Based Sequencing of Chillers (CSD Example)

59

VPF Systems Design/Control Considerations

60

Chillers Equal Sized Chillers preferred, but not required

Maintain Min flow rates with Bypass control (1.5 fps)

Maintain Max flow rates (11.0 to 12.0 fps) and max WPDs (45’ for 2P, 67’ for3P)

Modulating Isolation Valves (or 2-position stroke-able) set to open in 1.5 to 2min

Don’t vary flow too quickly through chillers (VSD pump Ramp rate – typical setting of10%/min)

Sequence

If CSD Chillers – Load-based sequencing…run chillers to max load (Supply Temp rise). Do not run more chillers than needed (water-cooled, single compressorassumed)

If VSD Chillers – Energy-based sequencing…run chillers between 30% and 80% load (depending on ECWT and actual off-design performance curves). Run more chillers than load requires.

Energy-Based Sequencing of Chillers (VSD Example)

85ºF, 56%

75ºF, 48%

65ºF, 39%

55ºF, 32%

61

When to Employ CPF Next step above unitary products (introductory chilled water)

Low First cost, low budget projects where energy is secondary

Small speculative office buildings (small single chiller plants)

When to Employ VPF Plants that serve a few close buildings

Plants where full CPO, maximum efficiency is required

More sophisticated owner/operators

When to Employ P/S District Cooling Plants or Large (College) Campuses

Central Plants that serve loads far away on different schedules

Projects where energy is more important than first cost

Where separated water loops are more apropos

Where greatest reliability is required

62

Application Considerations

AGENDA






Questions

63

Pressure enthalpy curve Basic refrigeration cycle

Refrigerant rejects heat to atmosphere

Refrigerant absorbs heat from load

Lift(or Head Pressure)

Pres

sure

Enthalpy

Evaporator

© 2020 Johnson Controls. All rights reserved.

Condenser

Metering Device

Centrifugal chillers in today’s complex buildings How they work

Pres

sure

Enthalpy

Lift(or Head Pressure)

54° F (12° C)

44° F (7° C)

85° F (29° C)

95° F (35° C)


How much energy is used?

Cooling Tower

5 hp/100 tons

Rul

es o

fthu

mb

Chilled Water Pump5 hp/100 tons

Condenser Water Pump5 hp/100 tons

Water-Cooled Chiller

75 hp/100 tons

Air-Cooled Chiller

140 hp/100 tons

500

ton

exam

ple Cooling Tower

25hp = 18kW


Chilled Water Pump

25hp = 18kW

Condenser Water Pump

25hp = 18kW


0.56kW/tr = 280kW

Air-Cooled Chiller10 EER = 1.2kW/tr

= 600kW

How much energy is used?

Chi

lled

Wat

erPl

ant

Com

pone

nts

500

ton

Cen

trifu

gal

Chi

llerP

lant



1500 gpm @ 60 wpd

27.1 BHP

Cooling Tower

Cooling Tower Fan(s)

30 BHP

Chilled Water Pump

Chilled Water Pump

850 gpm @ 100 wpd

25.4 BHP


500 ton Centrifugal Chiller

361 BHP

Total = 82.5 BHP


Chiller BHP = 4.4Xall other components

combined

Real world energy performanceHow does leaving chilled water temperature affect efficiency

Pres

sure

Evaporator

Condenser

Met

erin

gD

evic

e

∆ℎ

Energy / Enthalpy

Lift(or HeadPressure)



Real world energy performance Capitalizing on off-design conditions

Pres

sure

Energy / Enthalpy

Evaporator

Condenser

Met

erin

gD

evic

eReduces

energy consumption

Reduces compressor work

Lowershead pressure (lift)

RAISING chilled water temperature


∆ℎ

∆ℎ Energy$aved

Water temperatures and chiller efficiency

1°Fcolder leaving chilled water temperature (lchwt)

or1°Fwarmer leaving chilled water temperature (lchwt)

2.2%Loss/gain to chiller efficiency

Cooling Tower5hp/100ton

Pumps (2x)10hp/100ton

Chiller70-75hp/100ton

Chiller Plant Efficiency Impacts Average Power Use


Centrifugal plantsChilled water temperature and system efficiency


Example System Assumptions ECHWT/LCHWT Efficiency (kW/ton)

Variance (% Efficiency)

500 tons 42 / 56 0.603 and 0.363 NPLVCentrifugal Chiller 44 / 58 0.572 and 0.337 NPLV + 5.4% / + 7.7%85 / 95 degree condenserwater (3 gpm/ton) 45 / 59 0.561 and 0.325 NPLV + 7.5% / + 11.7%

42 / 52 0.606 and 0.363 NPLVDelta T has little effect on chiller efficiency 44 / 54 0.574 and 0.338 NPLV

45 / 55 0.560 and 0.326 NPLV

With constant equipment cost, you will improve system efficiency with warmer CHW design temps.

54 deg air is achievable w/ 45 deg Chilled Water Regardless of Entering Air Conditions

What temperature chilled water do I need?

8000 CFM, 500 fpm

Inlet Air EAT(wb/db) EWT/LWTLAT CHWFlow

CoolingCoil(wb/db) gpm

100% OutsideAir 95/78 45/59 53.5 / 53.4 92.7 8-row & 10 FPI

Mixed Air 80/67 45/59 53.6 / 53.1 47.0 6-row & 10FPI

100% Return Air 75/62 45/59 53.9 / 52.7 30.0 6-row & 9FPI

Centrifugal chiller plantsChilled water temps & system efficiency

Warmer chilled water temps do not significantly impact airside performance or cost.

LCHWT/ECHWT LAT db / LAT wbMinimum Cooling

Coil Required First Cost vs. 42/56

42 / 56 53.5 / 52.7 5-rows 9 FPI

44 / 58 53.5 / 52.9 6-rows 9 FPI + $239

45 / 59 53.6 / 53.1 6-rows 10 FPI + $283

Air pressure drop difference: 42 vs. 45 CHW = 0.16” wpd

Example Airside Impact80 / 67 Entering Mixed Air Temp for AHU cooling coil 8,000 CFM AHUs @ 500 fpm

LAT = Sub 54 (54 db / 53.5 wb)


Yearly system energy savings

Net System Energy Savings = $3,350, ~ 5.5% per year

Chiller: Chiller:

42 / 56 design, 0.363 kw/ton NPLV:45 / 59 design, 0.325 kw/ton NPLV:

$38,115 / year$34,125 / year

$3,990 reduction / year on Chiller

Airside: Airside:

42 / 56 design, 7.70 BHP per 8k CFMAHU: 45 / 59 design, 7.92 BHP per 8k CFMAHU:

$22,402 / year$23,042 / year

$640 extra / year on Airside

Assumptions: 500-ton chiller 3,000 yearly operating hours 350-ton average load $0.10/kwh 13 AHUs running at 8000 CFM (27-tons)

= 350-ton average load


Airside BHP based on AF Fan at 4.0” TSP vs. 4.16” TSP (0.16” apd increase)

Annual Chiller Energy Cost = (Avg Load) (Run Hours) (NPLV kw/ton) ($/kwh)

Annual Airside Energy Cost = (Qty AHUs) (Run Hours) (BHP) (0.746 kw/bhp) ($/kwh)

What is the bestleaving chilled water temperature (lchwt)

for system efficiency?

The warmest temperature capable of providing your desired airside leaving air temp.


Refrigeration cycleReal world energy performance

Pres

sure

Evaporator

Condenser

Met

erin

gD

evic

e


∆ℎ

Energy / Enthalpy



Refrigeration cycleCapitalizing on lower leaving condenser water temperatures

Pres

sure

Energy / Enthalpy

Evaporator

Met

erin

gD

evic

e

Condenser

∆ℎ ∆ℎ

LOWERING condenser water temperature

Lowers head pressure

Reduces compressor work

Reduces energy consumption


Energy$aved

Centrifugal chiller plantsCondenser water temperature and system efficiency

Entering condenser water temperature has minimal impact on efficiency

LEAVING condenser water temperature drives efficiency

Example:

3 gpm/ton 2 gpm/ton = 7.5% - 10%efficiency reduction

For every 1°F or 1°F the leaving CHW

temperature changes,

a chiller gains or looses≈ 1.5% - 2%in efficiency

Colderleaving condenser water temperature

saves energyandachieves airside performance


Centrifugal plantsCondenser water temperature and system efficiency

Chiller500 tons54/44°F chilled water 85°F ECWT

Although you are using more energy on the Condenser Pump at 3 GPM/ton (6.3 BHP), you are saving over 4 times that energy (28 BHP) by making the Chiller more efficient

FL Efficiency = 0.574 FL Efficiency = 0.619

IPLV = 0.338 IPLV = 0.364

Chiller BHP = 361 Chiller BHP = 389

Parameters 3 GPM/ton (1500 GPM) 2 GPM/ton (1000 GPM)

Pump BHP = 27.1 Pump BHP = 20.8Condenser Pump60 ft WPD


+28 BHPincrease

BHP change

-6.3 BHPdecrease

EB8

Diapositive 79

EB8 FL = Full load efficiency - (1%) - Ajouter slide Montréal ASHRAEEmilie Boyer, 2/8/2021

AGENDA






Questions

80

Centrifugal plantsCondenser water temps and system efficiency

800

Ton

Chi

ller

Sche

dule

Tow

erSc

hedu

lePu

mp

Sche

dule

Tower

Pump

Chiller

3 GPM/ton

3 GPM/ton



3 GPM/ton

Centrifugal plantsCondenser water temps and system efficiency 3 GPM/ton Rating


10° ΔT


3 GPM/ton 0.5727 0.3725 174032


3 GPM/ton 0.3725

Summary


RAISING leaving chilled water temperature saves energy Chiller gains/looses 2.0 – 2.5% efficiency with every degree

change in lchwt Negligible difference in chiller performance with higher

evaporator ΔT

LOWERING entering condenser water temperature saves energy Chiller gains/looses 1.5 – 2.0% efficiency with every degree

change in ecwt Major difference in chiller performance with higher condenser ΔT Leaving condenser water temperature sets chiller efficiency

HIGHER condenser flow saves chiller and system efficiency 3GPM/ton saves 7.5 – 10.0% efficiency vs 2 GPM/ton Review all component schedules during chiller selections

QUESTIONS?


Refroidisseur 101 2021.02.07

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Transcript of Refroidisseur 101 2021.02.07